Optical fiber cable

ABSTRACT

An optical communication cable is provided. The optical communication cable includes an outer cable layer and a plurality of optical fiber bundles surrounded by the outer cable layer. Each optical fiber bundle includes a bundle jacket surrounding a plurality of optical fiber subunits located within the bundle passage. The plurality of optical subunits are wrapped around each other within the bundle passage forming a wrapped pattern. Each optical fiber subunit includes a subunit jacket surrounding a elongate optical fiber located within the subunit passage. The cable jacket, bundle jacket and subunit jacket may be fire resistant, and strength strands of differing lengths may be located in the bundles and the subunits.

PRIORITY APPLICATION

This application is a divisional of U.S. application Ser. No.14/818,611, filed Aug. 5, 2015, which claims the benefit of priorityunder 35 U.S.C. § 119 of U.S. Provisional Application No. 62/035,016,filed on Aug. 8, 2014, and U.S. Provisional Application No. 62/053,340,filed on Sep. 22, 2014, the content of each of which is relied upon andincorporated herein by reference in their entirety.

BACKGROUND

The disclosure relates generally to optical communication cables andmore particularly to optical communication cables including multipleoptical fiber subunits. Optical communication cables have seen increaseduse in a wide variety of electronics and telecommunications fields.Optical communication cables contain or surround one or more opticalcommunication fibers. The cable provides structure and protection forthe optical fibers within the cable.

SUMMARY

One embodiment of the disclosure relates to an optical communicationcable. The optical communication cable includes an outer cable layer anda plurality of optical fiber bundles surrounded by the outer cablelayer. Each optical fiber bundle includes a bundle jacket defining abundle passage, a first tensile strength strand located within thebundle passage and a plurality of optical fiber subunits located withinthe bundle passage. The pluralities of optical subunits are wrappedaround each other within the bundle passage forming a wrapped pattern.Each optical fiber subunit includes a subunit jacket defining a subunitpassage, a second tensile strength strand located within the subunitpassage and an elongate optical fiber located within the subunitpassage. The first tensile strength strand of each optical fiber bundleis located outside of the jackets of the optical fiber subunits. Alength of the second tensile strength strand is substantially the sameas a length of the elongate optical fiber. A length of the first tensilestrength strand is less than the length of the second tensile strengthstrand and the length of the elongate optical fiber.

An additional embodiment of the disclosure relates to a high densityfire resistant optical communication cable. The cable includes a cablebody including a body passage within the cable body, and the cable bodyis formed from a fire resistant polymer material. The cable includes aplurality of optical fiber bundles located within the body passage. Eachoptical fiber bundle includes a bundle jacket formed from a fireresistant polymer material and defines a bundle passage. Each opticalfiber bundle includes a plurality of optical fiber subunits located withthe bundle passage. Each optical fiber subunit includes a subunit jacketformed from a fire resistant polymer material defining a subunit passageand a plurality of elongate optical fibers located within the subunitpassage. The plurality of optical fiber bundles includes an outer groupof optical fiber bundles and an inner group of optical fiber bundles,and the inner group of optical fiber bundles is wrapped around eachother forming a first wrapped pattern that includes at least onespirally wrapped section having a first pitch length. The outer group ofoptical fiber bundles surround and are wrapped around the inner group ofoptical fiber bundles forming a second wrapped pattern that includes atleast one spirally wrapped section having a second pitch length. Thesecond pitch length is greater than the first pitch length such that atotal length of each optical fiber of the outer group of optical fiberbundles is substantially the same as a total length of each opticalfiber of the inner group of optical fiber bundles within at least one 1meter length of the cable.

An additional embodiment of the disclosure relates to a high densityfire resistant optical communication cable. The cable includes a cablebody including a body passage within the cable body, and the cable bodyis formed from a fire resistant polymer material. The cable includes aplurality of optical fiber bundles located within the body passage. Eachoptical fiber bundle includes a bundle jacket formed from a fireresistant polymer material and defines a bundle passage. Each opticalfiber bundle includes a first tensile strength strand located andunstranded within the bundle passage and a plurality of optical fibersubunits located with the bundle passage. Each optical fiber subunitincludes a subunit jacket formed from a fire resistant polymer materialdefining a subunit passage, a second tensile strength strand located andunstranded within the subunit passage and a plurality of elongateoptical fibers located within the subunit passage. The plurality ofoptical fiber bundles includes an outer group of optical fiber bundlesand an inner group of optical fiber bundles, and the inner group ofoptical fiber bundles is wrapped around each other forming a firstwrapped pattern that includes at least one spirally wrapped sectionhaving a first pitch length. The outer group of optical fiber bundlessurround and are wrapped around the inner group of optical fiber bundlesforming a second wrapped pattern that includes at least one spirallywrapped section having a second pitch length. The second pitch length isgreater than the first pitch length such that a total length of eachoptical fiber of the outer group of optical fiber bundles issubstantially the same as a total length of each optical fiber of theinner group of optical fiber bundles. The first tensile strength strandof each optical fiber bundle is located outside of the subunit jackets.A length of each second tensile strength strand is substantially thesame as a length of the elongate optical fibers of the optical fibersubunit in which the second tensile strength strand is located. A lengthof each first tensile strength strand is less than the length of atleast one elongate optical fiber. The total number of elongate opticalfibers within the cable body is at least 288 and a greatest outerdimension of the cable body is less than 30 mm.

An additional embodiment of the disclosure relates to an opticalcommunication cable including outer cable layer and a first tensilestrength strand surrounded by the outer cable layer. The cable includesa plurality of optical transmission units surrounded by the outer cablelayer. Each optical transmission unit includes an inner jacket defininga passage, at least one elongate optical fiber located within thepassage and a second tensile strength strand located within the passage.The first tensile strength strand is located outside of the innerjackets of the optical transmission units. A length of the first tensilestrength strand is less than a length of the second tensile strengthstrands and is also less than a length of the elongate optical fiber ofeach of the optical transmission units.

An additional embodiment of the disclosure relates to opticalcommunication cable. The cable includes a cable body including a bodypassage within the cable body and a plurality of optical transmissionunits located within the body passage. Each optical transmission unitincludes at least one optical fiber. The plurality of opticaltransmission units include an outer group of optical transmission unitsand an inner group of optical transmission units. The inner group ofoptical transmission units is wrapped around each other forming a firstwrapped pattern that includes at least one spirally wrapped sectionhaving a first pitch length. The outer group of optical transmissionunits surround and are wrapped around the inner group of opticaltransmission units forming a second wrapped pattern that includes atleast one spirally wrapped section having a second pitch length. Thesecond pitch length is greater than the first pitch length such that atotal length of each optical fiber of the outer group of opticaltransmission units is substantially the same as a total length of eachoptical fiber of the inner group of optical transmission units within atleast one 1 meter length of the cable.

An additional embodiment of the disclosure relates to opticalcommunication cable assembly. The optical communication cable assemblyincludes an outer cable jacket, a plurality of first tensile strengthstrands surrounded by the outer cable jacket and a plurality of opticaltransmission units surrounded by the outer cable jacket. Each opticaltransmission unit includes an inner jacket defining a passage, at leastone elongate optical fiber located within the passage and a secondtensile strength strand located within the passage. The first tensilestrength strands are located outside of the inner jackets of the opticaltransmission units. Lengths of the first tensile strength strands areless than lengths of the second tensile strength strands and are lessthan lengths of the elongate optical fiber of each of the opticaltransmission units. The optical communication cable assembly includes afurcation plug. The outer cable jacket is coupled to a first end of thefurcation plug such that the outer cable jacket terminates at thefurcation plug and that each of the optical transmission units extendsout of a second end of the furcation plug such that an outer surface ofthe outer cable jacket defines an outermost surface of the assembly onan upstream side of the furcation plug. The first tensile strands arebonded to the furcation plug such that tension applied to the furcationplug is borne at least in part by the first tensile strength strands.

Additional features and advantages will be set forth in the detaileddescription that follows, and in part will be readily apparent to thoseskilled in the art from the description or recognized by practicing theembodiments as described in the written description and claims hereof,as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description are merely exemplary, and areintended to provide an overview or framework to understand the natureand character of the claims.

The accompanying drawings are included to provide a furtherunderstanding and are incorporated in and constitute a part of thisspecification. The drawings illustrate one or more embodiment(s), andtogether with the description serve to explain principles and theoperation of the various embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an optical fiber cable according to anexemplary embodiment.

FIG. 2 is a side view of the cable of FIG. 1 with the cable jacketremoved showing wrapped bundle groups according to an exemplaryembodiment.

FIG. 3 is a cross-sectional view of the cable of FIG. 1 according to anexemplary embodiment.

FIG. 4 is a cross-sectional view of a bundle of the cable of FIG. 1according to an exemplary embodiment.

FIG. 5 is a perspective view of the cable of FIG. 1 following furcationand connectorization according to an exemplary embodiment.

FIG. 6 is a cross-sectional view of a cable according to anotherexemplary embodiment.

FIG. 7 is a perspective view of an optical fiber cable according toanother exemplary embodiment.

FIG. 8 is a perspective view of an optical fiber cable according toanother exemplary embodiment.

FIG. 9 is a cross-sectional view of a cable according to anotherexemplary embodiment.

FIG. 10 is a cross-sectional view of a cable according to anotherexemplary embodiment.

FIG. 11 is a cross-sectional view of a cable according to anotherexemplary embodiment.

FIG. 12 is a cross-sectional view of a cable according to anotherexemplary embodiment; and

FIG. 13 is a perspective view of an optical fiber cable according toanother exemplary embodiment.

DETAILED DESCRIPTION

Referring generally to the figures, various embodiments of an opticalcommunication cable (e.g., a fiber optic cable, an optical fiber cable,etc.) are shown. In general, the cable embodiments disclosed herein areconfigured to support a large number of optical fibers within arelatively small space while, at least in some embodiments, providing ahigh level of fire resistance despite the large number of optic fiberslocated within the cable. In various embodiments, the cable embodimentsdisclosed herein include various structures that isolate tension appliedto the cable and that provide low latency or skew between differentfibers within the cable.

In various embodiments, the cable embodiments disclosed herein include aplurality of optical transmission units and each unit includes at leastone optical fiber. In some embodiments, the optical transmission unitsare optical fiber subunits each having a fire resistant subunit jacketsurrounding a plurality of optical fibers (e.g., twelve optical fibers).In some exemplary embodiments, the optical fiber subunits are located inan outer cable jacket and may be stranded within the cable jacketwithout intermediate jacket layers between the optical fiber subunitsand the outer cable jacket. In other embodiments, the opticaltransmission units are bundles of optical fiber subunits. In suchembodiments, the optical fiber subunits are grouped into a plurality ofbundles each including a plurality of optical fiber subunits surroundedby a fire resistant bundle jacket. In various embodiments, the bundlesare then surrounded by an outer cable layer, e.g., a cable jacket, madefrom a fire resistant material. In various embodiments, the three tieredlayers of fire resistant material provide a cable that passes variousfire rating tests (e.g., the plenum burn test, the riser burn test,etc.) despite supporting a large number of fibers (e.g., at least 192,fibers, at least 288 fibers) while at the same time allowing thethickness of the outer cable jacket to be relatively low.

In various embodiments, the optical transmission units are stranded orwrapped within the cable jacket. For example, in various embodiments,either optical fiber subunits or the bundles of optical fiber subunitsare stranded or wrapped around each other within the cable jacket. Invarious embodiments, the cable includes an inner group of opticaltransmission units (e.g., optical fiber subunits or optical fiberbundles of subunits) that are wrapped or twisted together and an outergroup of optical transmission units (e.g., optical fiber subunits oroptical fiber bundles of subunits) that are located outside of and arewrapped or twisted around the inner group. In various embodiments, thepitch of the wrapped pattern of each of the wrapped groups of opticaltransmission units are selected such that the optical fibers of theoptical transmission units of the outer group have substantially thesame total length as the optical fibers of the optical transmissionunits of the inner group.

Communications systems may use parallel optics schemes to increasesystem bandwidth. In such applications, the difference in the timebetween optical fibers for transmitting a signal from one end of thecable to the other end is called “skew.” For at least some paralleloptics schemes, low skew is an important property of the cable.Accordingly, in various embodiments of the cable of the presentdisclosure, the optical fibers within a subunit are substantially thesame length as each other such that there is low skew between theoptical fibers within a subunit. Furthermore, the subunits are uniformlystranded within each bundle such that the total length of the opticalfibers within a bundle are substantially the same as the other fiberswithin the bundle, which results in low skew between the optical fiberswithin a bundle.

In addition, in various embodiments, the pitch or “lay length” of thewrapped optical transmission units in the inner group is less than thepitch or “lay length” of the optical transmission units of the outergroup (e.g., meaning that the twist of the inner group is tighter thanthat of the outer group). In embodiments in which the opticaltransmission units include bundles of optical fiber subunits, the pitchor “lay length” of the wrapped bundles in the inner group is less thanthe pitch or “lay length” of the wrapped bundles of the outer group(e.g., meaning that the twist of the inner group is tighter than that ofthe outer group). In embodiments in which the optical transmission unitsinclude non-bundled optical fiber subunits, the pitch or “lay length” ofthe wrapped optical fiber subunits in the inner group is less than thepitch or “lay length” of the wrapped bundles of the outer group (e.g.,meaning that the twist of the inner group is tighter than that of theouter group). Thus, in these embodiments, the tighter twist of the innergroup accounts for the lower diameter of the inner group relative to theouter group such that the total length of the optical fiber subunitsand/or optical fibers within the subunits are substantially the samebetween the outer group and the inner group. In various embodiments, itis understood that the substantially equal optical fiber length betweenthe inner and outer groups results in an optical fiber cable with lowskew between fibers of the inner and outer groups, and in variousembodiments, the cable embodiments discussed herein are high densitycables for use with equipment that utilize cables with low skewcharacteristics. Further, the substantially equal length between fibersof the inner and outer groups also helps ensure that the fiber tensionthat is experienced is substantially evenly distributed across thefibers of the cable.

In addition, various cable embodiments discussed herein include twolevels of tensile strength strand or yarn strands (e.g., aramid strands)each having different lengths relative to each other. In variousembodiments, the different lengths of tensile strength yarns allow fordifferent tensions to be isolated and transmitted within the cable asmay be desired for different applications. For example in variousembodiments, the cable embodiments discussed herein include a first setof tensile strength strands located outside of each subunit jacket and asecond set of tensile strength strands located within each subunitjacket. In various embodiments, the first set of tensile strengthstrands are somewhat shorter in length than the optical fibers withinthe subunits, and the second set of tensile strength strands havesubstantially the same length as the optical fibers within the subunit.In specific embodiments in which the optical transmission units includebundles of optical fiber subunits, the first set of tensile strengthstrands may be located within each bundle jacket or within the cablejacket but outside of each subunit jacket and the second set of tensilestrength strands are located within each subunit jacket. In specificembodiments in which the optical transmission units include unbundledoptical fiber subunits, the first set of tensile strength strands may belocated outside of each subunit jacket but within the passage defined bythe cable jacket and the second set of tensile strength strands arelocated within each subunit jacket.

As will be explained in more detail below, a furcation body or plug maybe coupled to the cable to split the optical fiber subunits out from thecable body to optical fiber connectors that can then allow the fibers tobe connected to various pieces of equipment. In such embodiments, thefirst set of tensile strength strands may be coupled to the furcationbody. Because the tensile strength strands of the first set are shorterthan the optical fibers, the first set of tensile strength strands actsto isolate tension within the cable and allows pulling equipment toengage and pull on the furcation body such that the tension caused bypulling is transmitted through the first set of tensile strength strandsrather than in the optical fibers.

Further, the second set of tensile strength strands may be coupled tothe optical fiber connectors located at the end of each optical fibersubunit split out from the outer cable jacket at the furcation body.Coupling the second set of tensile strength strands (that are the samelength as the optical fibers) acts to limit the amount tension on theoptical fibers when installing the connectors in equipment racks. Thus,it is believed that the differential length of the two sets of tensilestrength strands discussed herein result in a cable and a cable assemblywith improved tension distribution characteristics.

Referring to FIGS. 1 and 2, an optical communication cable, shown ascable 10, is shown according to an exemplary embodiment. Cable 10includes an outer cable layer, shown as a cable body or cable jacket 12,having an inner surface 14 that defines an inner passage or cavity,shown as central bore 16. As will be generally understood, inner surface14 of jacket 12 defines an internal area or region within which thevarious cable components discussed below are located.

In various embodiments, cable 10 is a high density optical fiber cablethat includes a large number of optical fibers in a cable with arelatively low cross-sectional area. In such embodiments, cable 10includes a plurality of optical transmission units, shown as opticalfiber bundles 20. In general, as explained in more detail below, eachbundle 20 includes a plurality of optical fiber subunits, shown assubunits 50, and, in the specific embodiment shown, each bundle 20includes four subunits 50. Each subunit 50 includes a plurality ofindividual elongate optical transmission elements, shown as opticalfibers 58, and in the specific embodiment shown, each subunit 50includes 12 individual optical fibers 58.

As shown in FIG. 1 and FIG. 2, cable 10 includes an outer group 24 ofbundles 20 and an inner group 26 of bundles 20. In general, inner group26 is located generally in the central region of bore 16, and outergroup 24 is located around and surrounding inner group 26. In thespecific embodiment shown, cable 10 includes three bundles 20 withininner group 26 and nine bundles 20 within outer group 24. In otherembodiments, inner group 26 may include two, four, five, etc. bundles 20and outer group 24 may include less than nine bundles 20 or more thannine bundles 20. While the embodiments discussed herein relate primarilyto a cable having two groups (an inner group and an outer group) ofbundles 20, in other embodiments, cable 10 may include three, four, fiveor more concentric groups of bundles 20.

As shown best in FIG. 2, in various embodiments, both inner group 26 andouter group 24 of optical fiber bundles 20 are wrapped, twisted orstranded to form a wrapped pattern within bore 16. As shown in FIG. 2,bundles 20 of inner group 26 are wrapped around each other forming afirst wrapped pattern, and bundles 20 of outer group 24 are wrappedaround inner group 26 forming a second wrapped pattern. In variousembodiments, the first wrapped pattern and second wrapped pattern eachinclude at least one spirally wrapped or twisted portion. In variousembodiments, the first wrapped pattern of inner group 26 is differentfrom the second wrapped pattern of outer group 24. In general, thewrapped patterns of inner group 26 and outer group 24 are selected suchthat the lengths of the bundles 20 (and consequently of the opticalfibers within each bundle 20) are substantially the same as the otherbundles 20 and other fibers of cable 10 (e.g., lengths of all bundlesand all fibers of cable 10 are within 1.5% of each other and morespecifically within 0.1% of each other, as discussed in more detailbelow).

In general, the equal lengths between the inner group 26 and outer group24 are achieved through the inner group 26 having a tighter spiralpattern than outer group 24, and thus the tighter wrapped pattern ofinner group 26 accounts for the smaller diameter of group 26 as comparedto outer group 24 resulting in the substantially same lengths of bundles20 and fibers between inner group 26 and outer group 24. In a specificembodiment, the wrapped patterns of inner group 26 and outer group 24are selected such that the lengths of the bundles 20 of each group aresubstantially the same as the other bundles 20 within at least one, 1meter section of cable 10.

In various embodiments, the differential wrapping between inner group 26and outer group 24 provide for a cable 10 that allows for a high fiberdensity cable with characteristics suitable for use in indoor datacenter applications. The substantially equal length of bundles 20 (andof optical fibers within the bundles) between inner group 26 and outergroup 24 results in a cable 10 with relatively low skew between thefibers of different bundles 20. This may facilitate usage of cable 10 inconjunction with certain data center communications equipment, forexample parallel optics transmission equipment. In various embodiments,this stranding arrangement results in a cable 10 that has relatively lowskew meaning that the difference in transit time for opticalcommunication signals traveling in the optical fibers of outer group 24versus the transmit time for optical communication signals traveling inthe optical fibers of inner group 26 is less than 20 picoseconds/meterof cable (ps/m) and more specifically is less than 10 ps/m. In addition,the substantially equal length of bundles 20 (and of optical fiberswithin the bundles) between inner group 26 and outer group 24 resultssubstantially even tension distribution between the optical fibers ofouter group 24 and inner group 26.

As noted above and shown in FIG. 2, inner group 26 includes at least onespiral wrapped section 28, and outer group 24 includes at least onespiral wrapped section 30. Each spirally wrapped section includes apitch length (also known as lay length) which is the axial distancerequired for one of the bundles 20 to complete a full revolution withinthe spiral pattern. In some embodiments, inner group 26 and outer group24 has an average pitch length (or average lay length) which is theaverage of the multiple individual pitch lengths along the length ofcable 10.

In various embodiments, the pitch length of at least one spiral wrappedsection of inner group 26 is between 125 mm and 350 mm, specifically isbetween 150 mm and 250 mm, and more specifically is between 175 mm and225 mm. In such embodiments, the pitch length of at least one spiralwrapped section of outer group 24 is between 300 mm and 900 mm,specifically is between 400 mm and 600 mm, and more specifically isbetween 450 mm and 550 mm. In a specific embodiment, the pitch length ofat least one spiral wrapped section of inner group 26 is between 175 mmand 225 mm and the pitch length of at least one spiral wrapped sectionof outer group 24 is between 450 mm and 550 mm. In another specificembodiment, the pitch length of at least one spiral wrapped section ofinner group 26 is between 195 mm and 205 mm and the pitch length of atleast one spiral wrapped section of outer group 24 is between 505 mm and515 mm.

In various embodiments, the differential stranding or wrapping of innergroup 26 and outer group 24 results in a relatively low lengthdifference (e.g., excess bundle length) between outer group 24 and innergroup 26 such that the lengths of bundles 20 are substantially the samebetween outer group 24 and inner group 26. In various embodiments, thepercentage length difference between the bundles 20 of outer group 24and the respective optical fibers of outer group 24 and the bundles 20of inner group 26 and the respective optical fibers of inner group 26 isless than 0.6%, specifically is less than 0.3% and more specifically isbetween 0.05% and 0.15%.

Various specific embodiments of a cable 10 having differential spiralwrapping between inner group 26 and outer group 24 are shown in theTable 1 below for a bundles with a diameter of 5.6 mm Similar tables maybe constructed for bundles having different diameters.

TABLE 1 Average Pitch or Lay Length Difference in Length of Inner GroupOuter Group Bundles Compared to 26 (mm) 24 (mm) Length Cable 10 (%) 350891 0.18 300 764 0.24 250 636 0.34 200 509 0.54 175 445 0.70 150 3820.95 138 350 1.13 125 318 1.37

Table 1 shows the differences between the cable length and bundle lengthfor exemplary embodiments of cable 10 having bundles with a diameter of5.6 mm. Typical stranding for cables of this size would be to use a 350mm lay length for both layers of the cable. For such strandingparameters, the inner layer 26 would be 0.18% longer than the cable, andthe outer layer would be 1.13% longer than the cable. Such strandingwould result in the optical fibers in the outer layer being 0.95% longerthan the optical fibers in the inner layer (that is 1.13%−0.18%=0.95%).Because the lay lengths of the inner group and outer group of bundles 20of cable 10 are different, as discussed above, the fiber length betweenthe outer bundle 24 and the inner bundle 26 is balanced. For example, ifthe outer bundle 24 has a lay length of 350 mm, then the inner bundle 26would have a lay length of 138 mm to balance the optical fiber lengths.In general, long lay lengths make the cable less flexible and short laylengths reduce production speed. Table 1 shows a range of paired laylengths from which to choose to obtain desired cable properties.

A number of different wrapped patterns may be used to form outer layer24 and inner layer 26. In various embodiments, outer layer 24 and innerlayer 26 are wrapped in an SZ wrapped pattern (also referred to as an SZstranding pattern). In such embodiments, outer layer 24 and inner layer26 include right-handed spirally wrapped sections, reversal sections andleft-handed spirally sections. Within right-handed spirally wrappedsections, bundles 20 are wrapped spirally in the right-handed direction.Within left-handed spirally wrapped sections, bundles 20 are wrappedspirally in the left-handed direction. Reversal sections 32 are thesections that provide the transition between the right-handed spirallywrapped sections and the left-handed spirally wrapped sections. In someembodiments, as shown in FIG. 2, the reversal sections 32 are shaped asa sinusoidal function. In various embodiments, the at least one spirallywrapped section of the wrapped pattern of inner group 26 and outer group24 may be either the left-handed or right-handed spirally wrappedsections of the SZ stranding pattern shown, and may have any of thepitch lengths discussed herein.

It should be understood that while FIG. 2 shows one right-handedspirally wrapped section, one reversal section and one left-handedspirally wrapped section, inner group 26 and outer group 24 may includea large number of repeating sections similar to the sections shown inFIG. 2. In various embodiments, the right-handed spirally wrappedsections and left-handed spirally wrapped sections alternate along thelength of cable with reversal sections located between each oppositelywrapped spiral section. In other embodiments, inner group 26 and outergroup 24 may be wrapped in non-reversing spiral or helical patternshaving any of the pitch lengths discussed herein.

Referring to FIG. 3 and FIG. 4, the structure of cable 10 is shown inmore detail. As shown in FIG. 3, cable 10 includes a plurality ofbundles 20 (e.g., twelve bundles 20 in the specific embodiment shown)located within bore 16 defined by cable jacket 12. Each bundle 20includes an outer layer or bundle jacket 40 that has an inner surface 42that defines a bundle passage or bore 44. Each bundle 20 includes atleast one or a plurality of optical fiber subunits, shown as subunits50, located within bundle passage 44. Each subunit 50 includes an innerjacket or subunit jacket, shown as subunit sheath 52, having an innersurface 54 defining a subunit passage or bore 56. A plurality ofindividual, elongate optical transmission elements, shown as opticalfibers 58 are located within bore 56 of each subunit 50.

In various embodiments, cable jacket 12, bundle jacket 40 and subunitsheath 52 are each formed from an extrudable or extruded polymermaterial of sufficient strength to hold together each unit of cable 10as discussed herein. In various embodiments, cable jacket 12 providesfor structure and support for cable 10, and bundle jacket 40 may be thinenough to allow for access to subunits 50 without the need for cuttingtools. In various embodiments, cable jacket 12 may include an accessfeature, such as one or more frangible sections or ripcords, that allowsa user to open cable jacket 12 with relative ease in order to accessbundles 20 and subunits 50. In accordance with yet other aspects of thedisclosure, the bundle jacket 40 may be made from a low strengthmaterial with a thin wall such that one may remove the bundle jacket bysimply tearing it with the fingers. In various embodiments, bundlejacket 40 and/or subunit sheath 52 may be formed from a helicallywrapped binder yarn. In various embodiments, subunit 50 may containwater swellable powders, threads or tapes to impart water blockingcapability to the subunit.

In various embodiments, the function of the bundle jacket is to hold thesubunits within the bundle together so they form a cohesive unit thatmight pass through processing equipment to be placed within the cablecavity 16. In various embodiments, this function may also be fulfilledby helically stranding the subunits with a tight twist (e.g. like arope) so that they form a cohesive unit or bundle for processing.

In various embodiments, bundle jacket 40 may be an extruded thin filmthat cools to provide an inwardly directed force on to subunits 50. Theinwardly directed force provided by this embodiment of bundle jacket 40assists to hold subunits 50 together. For example, the inwardly directedforce provided by bundle jacket 40 may act to prevent/resist unravelingof the wound subunits 50.

As discussed above, bundles 20 are wrapped or stranded within bore 16 ofcable jacket 12. In addition to the bundle level stranding, subunits 50are wrapped or stranded around each other within each bundle 20. In suchembodiments, subunits 50 are wrapped to include at least one spirallywrapped section, and specifically may be SZ stranded as discussed aboveregarding stranding of bundles 20. In various embodiments, subunits 50may be wrapped in a pattern such that the pitch length of the wrappedsubunits 50 is between 85 mm and 1000 mm, specifically between 200 mmand 400 mm. In various embodiments, the tensile strands 60 within eachbundle 20 are substantially parallel to the axis of the bundle or areintroduced into the bundle without wrapping or stranding thereby makingthe tensile strands within the bundle shorter than the subunits andoptical fibers. In various embodiments the bundles may contain waterswellable powders, threads, or tapes to impart water blocking capabilityto the bundles.

In various embodiments, the two stranding levels of cable 10 results ina cable in which the total axial length of subunits 50 is greater thanthe total axial length of the surrounding bundle 20 (and specifically ofthe bundle jacket 40), and the total axial length of bundles 20 isgreater than the total axial length of cable 10 (and specifically cablejacket 12). In addition, in such embodiments, optical fibers 58 are notstranded within subunit sheath 52, and in such embodiments, the totalaxial length of optical fibers 58 is substantially the same (e.g.,within less than 0.1% of each other) as the axial length of therespective subunit 50 (and specifically subunit sheath 52).

In various embodiments, cable 10 is fire resistant cable suitable forindoor use. In various embodiments, cable 10 includes materials and isdesigned to pass the plenum burn test (NFPA 262) and/or the riser burntest (UL1666). In another embodiment, cable 10 is a fire-resistant,non-corrosive cable (IEC 60332 3). In another embodiment, the opticalcommunication cable achieves at least a Class Dca rating with theEuropean construction products regulation for fire safety when tested toEN50339, EN61034-2, EN60754-2, and EN60332-1-2-3 and achieved a ClassDca rating, or more preferably a Class Cca rating, or more preferably aclass B2ca rating as described in the standards. In various embodiments,optical fibers 58 include an outer protective coating, such as aUV-cured urethane acrylate materials, that act to protect the innerglass fiber. However, these outer coating materials may generatesignificant heat when exposed to fire such that as the optical fibercount and optical fiber density of a particular cable increase, the burnresistance of the cable 10 tends to decrease. However, in variousembodiments, cable 10 is specifically structured to provide a high fibercount, high fiber density cable while still maintaining satisfactoryburn resistance characteristics.

In such fire resistant embodiments of cable 10, cable jacket 12, bundlejacket 40 and subunit sheath 52 are all formed from a fire resistantmaterial, such as an extrudable fire resistant polymer material. Invarious embodiments, by utilizing multiple layers of fire resistantjacket materials within cable 10, cable 10 is able to pass the variousfire resistance tests discussed above despite the large number of fibersand high fiber density of cable 10. In addition, by utilizing multiplelayers of fire resistant jacket materials within cable 10, the overallcross-sectional area, outer diameter of cable 10 and the thickness ofcable jacket 12 are reduced as compared to other high number fibercables without the multi-layer fire resistant design of cable 10.

In various embodiments, cable jacket 12, bundle jacket 40 and subunitsheath 52 are formed from an extrudable polymer material that includesone or more material, additive or component embedded in the polymermaterial that provides fire resistant characteristics such as relativelylow heat generation, low heat propagation, low flame propagation, lowsmoke production. In various embodiments, the fire resistant materialmay include an intumescent material additive embedded in the polymermaterial. In other embodiments, the fire resistant material includes anon-intumescent fire resistant material embedded in the polymermaterial, such as a metal hydroxide, aluminum hydroxide, magnesiumhydroxide, etc., that produces water in the presence of heat/fire whichslows or limits heat transfer through cable 10. In specific embodiments,the fire resistant material may be a low smoke zero halogen polymermaterial.

In various embodiments, cable jacket 12, bundle jacket 40 and subunitsheath 52 may include particles of intumescent material embedded in thematerial of the cable jacket forming an intumescent layer that coats theinner surface of the respective jacket. In this embodiment, as heat istransferred through each jacket layer, the intumescent material expandsblocking air flow through the bore of the respective jacket layer. Theintumescent material also forms a char layer that has low heatconductivity further limiting heat penetration into the middle of thecable. In various embodiments, the intumescent material may includesodium silicates, graphite or one or more of the Exolit materialsavailable from Clariant. In various embodiments, the fire resistantmaterial may be a fire resistant polyethylene, polypropylene, PVC, orany suitable fire resistant polymer material used in optical fiber cableconstruction.

In various embodiments, cable jacket 12, bundle jacket 40 and subunitsheath 52 may each be formed from the same fire resistant material, andin other embodiments, cable jacket 12, bundle jacket 40 and subunitsheath 52 may each be formed from different fire resistant materials aseach other. In various embodiments, at least one of cable jacket 12,bundle jacket 40 and subunit sheath 52 may be formed from a fireresistant material and at least one of cable jacket 12, bundle jacket 40and subunit sheath 52 may be formed from a non-fire resistant material.In various embodiments, water swellable powders, tapes, or yarns may beplaced within jacket 12 to impart water blocking capability to thecable.

In certain embodiments, the fire resistant material of cable jacket 12,bundle jacket 40 and subunit sheath 52 may be a highly-filled polymermaterial with a limiting oxygen index (LOI) of 54 or higher. However inother embodiments, cable jacket 12, bundle jacket 40 and subunit sheath52 may be formed from a less highly-filled jacket material with an LOIof 48 or less and may utilize embedded intumescent materials, fireretardant tapes, etc. to provide the desired fire resistant properties.In such embodiments, cable 10 may include a fire retardant tape, such asmica tape, wrapped around and outside of bundles 20.

In various embodiments, cable jacket 12 has a thickness shown as T1,bundle jacket 40 has a thickness shown as T2 and subunit sheath 52 has athickness shown as T3. In various embodiments, T1 is between 0.1 mm and3 mm, specifically is between 0.5 mm and 1.5 mm and more specifically isabout 1.0 mm (1.0 mm plus or minus 0.1 mm). In various embodiments, T2is between 0.1 mm and 0.8 mm, specifically is between 0.2 mm and 0.6 mmand more specifically is about 0.4 mm. In various embodiments, T3 isbetween 0.1 mm and 1.0 mm, specifically is between 0.2 mm and 0.6 mm andmore specifically is about 0.3 mm. In various embodiments, by utilizingthe three distinct fire resistant layers, the total thickness of cablejacket 12 may be smaller than is typically needed to pass one or more ofthe burn tests discussed above with a cable having a high number ofoptical fibers that relies only on outer layers for fire resistance.

In the embodiment shown, cable 10 is configured to hold 576 totaloptical fibers 58. In such embodiments, cable 10 includes twelve bundles20, and each bundle 20 includes four subunits 50 such that cable 10includes 48 total subunits 50. In such embodiments, each subunit 50includes twelve optical fibers 58. In this embodiment, each bundle 20 isconfigured to be coupled to a 48 fiber connector at the upstream end ofcable 10, and each subunit 50 is configured to be coupled to a 12 fiberconnector (e.g., connector 76 discussed below) at the downstream end ofcable 10.

In other embodiments, cable 10 may support various numbers of bundles 20each including various numbers of subunits 50 each including variousnumbers of optical fibers 58. In various embodiments, cable 10 mayinclude 6, 8, 10, 14, 16, 20, etc. bundles 20, and each bundle 20 mayinclude 2, 3, 5, 6, 8, 10 etc. subunits 50, and each subunit 50 mayinclude 2, 4, 6, 8, 10, 14, 16, 20, 28, 32, etc. optical fibers 58. Inone embodiment, each bundle 20 includes two, twelve optical fibersubunits, and the upstream end of cable 10 is configured to be coupledto a 24 fiber connector. In another embodiment, each bundle 20 includesthree, twelve optical fiber subunits, and the upstream end of cable 10is configured to be coupled to a 36 fiber connector. In anotherembodiment, each bundle 20 includes six, twelve optical fiber subunits,and the upstream end of cable 10 is configured to be coupled to a 76fiber connector. In another embodiment, each bundle 20 includes eight,twelve optical fiber subunits, and the upstream end of cable 10 isconfigured to be coupled to a 96 fiber connector.

In various embodiments, the maximum outer dimension of cable jacket 12,shown as the outer diameter, D1, of cable jacket 12 is smaller than istypically needed to provide a cable with this large number of opticalfibers and providing satisfactory fire resistant characteristics. Invarious embodiments, D1 is less than 30 mm, specifically is less than 28mm and more specifically is less than 26 mm. In various embodiments,cable 10 includes at least 288 optical fibers 58 and the outer diameterof cable jacket 12 is less than 30 mm, and in another embodiment, cable10 includes at least 500 optical fibers 58 and the outer diameter ofcable jacket 12 is less than 30 mm. In a specific embodiment, cable 10includes 576 optical fibers 58 and the outer diameter of cable jacket 12is less than 30 mm. In various embodiments, bundles 20 each have anouter diameter shown as D2, and in various embodiments, D2 is between 4mm and 7 mm, specifically is between 5 mm and 6 mm and more specificallyis about 5.6 mm (e.g., 5.6 mm plus or minus 0.2 mm).

In addition to providing a high fiber count in a relatively compact,fire resistant cable, cable 10 may also be structured to provide fortension isolation allowing cable 10 to be used in conjunction withfurcation structures and optical fiber connectors that may facilitateuse of cable 10 within a datacenter. In general cable 10 includes atleast two distinct groups of tensile strength strands or yarns withincable 10. As shown best in FIG. 4, cable 10 includes at least one firsttensile strength strand, shown as bundle yarn 60, in each bundle 20, andat least one second tensile strength strand, shown as subunit yarn 62,located in each subunit 50. In various embodiments, tensile strands orrigid rods may be added within bore 16 but outside of bundles 20.

Bundle yarn 60 is located inside of bundle jacket 40 but outside ofsubunit sheaths 52, and subunit yarn 62 is located inside of subunitsheath 52. It should be understood that while FIG. 4 shows one bundleyarn 60 located within each bundle 20 and one subunit yarn 62 located ineach subunit 50, more than one bundle yarn 60 may be located in eachbundle 20 and more than one subunit yarn 62 may be located in eachsubunit 50. In various embodiments, use of bundle yarn 60 and/or subunityarn 62 allows cable 10 to be formed without a central strength member,such as a glass-reinforced plastic (GRP) rod, present in the center ofmany optical fiber cables.

In various embodiments, bundle yarn 60 is unstranded (e.g., is notwrapped around the outside of subunits 50) within each bundle 20 suchthat bundle yarn 60 is substantially the same length as bundle 20 andspecifically bundle jacket 40. As will be understood, in thisarrangement, because bundles 20 are stranded in a wrapped pattern andbecause subunits 50 are stranded in a wrapped pattern within each bundle20, the total axial length of bundle yarn 60 is less than the totalaxial length of subunits 50 and is less than the total axial length ofoptical fibers 58 within each subunit. In various embodiments, the totalaxial length of bundle yarn 60 is between 0.05% and 0.4% and morespecifically between 0.1% and 0.2% less than the total axial length ofsubunits 50 and the total axial length of optical fibers 58 within eachsubunit. As explained in more detail below, this arrangement results ina cable in which tension applied to the cable is primarily transmittedby and experienced by bundle yarn 60 rather than optical fibers 58.

As shown in FIGS. 3 and 4, cables may be formed with nine bundlesstranded around three bundles. In order to produce cables of variousfiber counts and maintain the 9-over-3 stranding, the bundles 20 mayhave either three or four or more subunits 50 within a bundle. Somecable designs incorporate fiber counts that do not lend themselves totwelve uniformly sized bundles. For these cables, filler rods may beused to replace some of the subunits 50. For example, to achieve a cablewith 384 fibers, then the cable shown in FIG. 4 could be made with fourof the subunits 50 replaced by filler rods. The filler rods may beeither solid rods of the appropriate fire retardant material or simply asubunit that contains no optical fibers.

In various embodiments, subunit yarn 62 is unstranded (e.g., is notwrapped around the outside of optical fibers 58) within each subunit 50such that subunit yarn 62 is substantially the same length as eachsubunit 50 and specifically subunits sheath 52. As will be understood,in this arrangement, because optical fibers 58 are similarly unstrandedwithin subunit 50, the total axial length of subunit yarn 62 within eachsubunit 50 is substantially the same as the total axial length ofoptical fibers 58 within each subunit. In such embodiments, the totalaxial length of subunit yarn 62 is within 0.1% and more specificallywithin 0.05% of the total axial length of optical fibers 58. Asexplained in more detail below, this arrangement results in a cable inwhich tension applied to the cable is isolated upstream from a furcationbody and evenly distributes tension experienced by the opticalconnectors coupled to the subunits.

In various embodiments, bundle yarn 60 and subunit yarn 62 may be anysuitable tensile strength yarn or fiber material used in cableconstruction. In various embodiments, bundle yarn 60 and subunit yarn 62are formed from an aramid yarn material. In other embodiments, thetensile strength strands of cable 10 may be fiberglass yarn,poly(p-phenylene-2,6-benzobisoxazole) yarn sold under the trade Zylon,polyester-polyarylate liquid crystal polymer fiber sold under the tradename Vectran, or other high strength tensile yarns.

FIG. 5 shows a cable assembly 71 formed with cable 10 after access ofsubunits 50 prior to connection to datacenter equipment. As shown toaccess subunits 50, a furcation body or plug 70 is coupled to cable 10.In general, furcation plug 70 is mounted to cable 10 allowing opticalfibers or in the case of cable 10, subunits 50, to be accessed forconnectorization and coupling to equipment. Cable 10 is received intofurcation plug 70, and furcation plug 70 is coupled to cable 10.

To couple furcation plug 70 to cable 10, a portion of cable jacket 12 isremoved exposing subunits 50. In this arrangement, on the upstream side72 of furcation plug 70, cable 10 is intact such that the outer surfaceof jacket 12 defines the outer surface of cable 10 on upstream side 72.On the downstream side 74 of furcation plug 70, cable jacket 12 andbundle jackets 40 have been removed exposing each subunit 50. In thisarrangement, the outer surfaces of subunit sheaths 52 define the outersurfaces of cable 10 on the downstream side of furcation plug 70.

Fiber optic connectors 76 are coupled to the downstream ends of subunits50. In general, each fiber optic connector 76 is coupled to each opticalfiber 58 of the subunit 50 to which it is attached, and connector 76facilitates connection of optical fibers 58 to the various datacenterequipment that cable 10 services. Accordingly, in the embodiment shown,connector 76 is a 12 fiber connector configured to communicate signalsfrom each of the twelve optical fibers of the respective subunit 50.

In such embodiments, separate furcation legs do not need to be installedto support optical fibers 58 because subunit sheaths 52 are sufficientlyrobust to provide for protection of optical fibers 58 following removalof cable jacket 12 and bundle jacket 40. In addition, subunit sheaths 52are sufficiently robust to support coupling of connectors 76.

As noted above, the length of bundle yarn strands 60 relative to thelength of optical fibers 58 acts such that bundle yarn strands 60 beartensile forces rather than optical fibers 58. Specifically, in variousembodiments, when furcation plug 70 is installed onto cable 10, bundleyarn strands 60 are coupled or locked onto furcation plug 70. In variousembodiments, an adhesive material such as epoxy is used to bond bundleyarn strands 60 to furcation plug 70. Thus, in this arrangement, tensionthat is applied to furcation plug 70 (e.g., via cable pulling equipmentsuch as a pulling grip) is borne through bundle yarn strands 60 ratherthan through optical fibers 58, and in addition, this arrangement actsto isolate tension within cable 10 to the upstream side 72 of plug 70.This isolation of tension limits the effects of cable tension on theexposed subunits 50 on the downstream side 74 of cable 10.

Further, the length of subunit yarn strands 62 relative to the length ofsubunits 50 acts to evenly distribute tension within the subunits 50 andthe tension experienced by connectors 76. In various embodiments, whenconnectors 76 are installed on to subunits 50, subunit yarn strand 62 ofeach subunits coupled to or locked onto connector 76. In variousembodiments, subunit yarn strands 62 are held on to the back ofconnectors 76 with a crimp band. Coupling of subunit yarn strands 62 toconnectors 76 limits the transfer of forces from optical fibers 58 toconnector 76 and thereby provides strain relief to connector 76.

In another embodiment, cable 10 may include additional tensile strengthyarns similar to bundle yarn 60 discussed above, except that theadditional yarns are located outside of bundle jackets 40 but inside ofcable jacket 12. In such embodiments, the additional tensile strengthyarns may be coupled directly to furcation plug 70, which in turn allowsbundles 20 to act as the furcation leg of cable 10 (instead of subunits50). In such embodiments, downstream connectors 76 may then be coupleddirectly to each bundle 20, and may be larger fiber connectors such as24, 36, 48, 72, 96 fiber connectors. In another embodiment, cable 10 mayinclude one or more GRP rods that are coupled to the furcation plug 70.

Referring to FIG. 6, an optical fiber cable 100 is shown according to anexemplary embodiment. Cable 100 is substantially the same as cable 10except as discussed herein. Cable 100 is a 432 fiber cable that includestwelve bundles 20 that each contain three subunits 50 each containingtwelve optical fibers 58.

Referring to FIG. 7, an optical fiber cable 110 is shown according to anexemplary embodiment. Cable 110 is substantially the same as cable 10except as discussed herein. Cable 110 is shown as an outdoor orindoor/outdoor cable including the bundle arrangement and tensile yarnarrangements discussed herein. Cable 110 includes a water blockinglayer, shown as water blocking tape 112, that surrounds bundles 20. Invarious embodiments, the water blocking layer may be a water blockingfoam, gel, woven or non-woven material. Cable 110 also includes areinforcement sheet or layer, shown as armor layer 114, that is locatedoutside of water blocking tape 112. Armor layer 114 is wrapped aroundthe interior elements (including bundles 20) of cable 110 such thatarmor layer 114 surrounds optical fibers 58. Armor layer 114 generallyprovides an additional layer of protection to optical fibers 58 withincable 110, and may provide resistance against damage (e.g., damagecaused by contact or compression during installation, damage from theelements, or damage from rodents, etc.).

In various embodiments, armor layer 114 is formed from a corrugatedsheet of metal material having an alternating series of ridges andtroughs. In one embodiment, the corrugated metal is steel. In otherembodiments, other non-metallic strengthening materials may be used. Forexample, armor layer 114 may be formed from fiberglass yarns (e.g.,coated fiberglass yarns, rovings, etc.). In some embodiments, armorlayer 114 may be formed from plastic materials having a modulus ofelasticity over 2 GPa, and more specifically over 2.7 GPa. Such plasticarmor layers may be used to resist animal gnawing and may includeanimal/pest repellant materials (e.g., a bitter material, a peppermaterial, synthetic tiger urine, etc.). In various embodiments, inaddition to water blocking tape 112, a layer of powder, such as waterabsorbing powder or particles, such as super absorbent polymer (SAP),SAP yarns or a water swellable gel or liquid, is located within bore 16of cable 110.

Cable 110 may also include one or more access features 116 embedded inthe material of cable jacket 12. In general, access features 116 areelongate members or structures embedded within the material of cablejacket 12. In one embodiment, access feature 116 is a discontinuouspolymer feature coextruded with the material of cable jacket 12. In thisembodiment, access feature 116 is formed from a polymer material that isdifferent from the material of jacket 12, and the difference inmaterials provides a discontinuity or weakness within cable jacket 12 atthe location of access features 116. In another embodiment, accessfeature 116 is a ripcord or wire embedded in cable jacket 12 thatfacilitates opening of cable jacket 12.

Referring to FIG. 8, an optical fiber cable 120 is shown according to anexemplary embodiment. Cable 120 is substantially the same as cable 10except as discussed herein. In this embodiment, cable 120 includes anouter cable layer, shown as binder 122. In one embodiment, binder 122 isan extruded thin film material that cools and provides an inwardlydirected force onto bundles 20 assisting in holding bundles 20 togetherin the wrapped pattern shown. In other embodiments, binder 122 may be alayer of helically wound binder yarn, binder thread or binder tape. Inthis embodiment, cable 120 does not include a thicker outer cablejacket, such as cable jacket 12, discussed above.

Referring to FIGS. 9-11, additional embodiments of an optical fibercable are shown. In general, the cable embodiments shown in FIGS. 9-11,include optical transmission units, shown as subunits 50, that areunbundled within cable jacket 12. In such embodiments, the cables do notinclude bundle jackets, and as explained in more detail below, the cableembodiments of FIGS. 9-11 include tensile strength strands 160 that arelocated within cable jacket 12 and outside of subunits 50 without beingbundled within a bundle jacket, but are otherwise substantially the sameas and function in the same manner as bundle yarn strands 60 discussedabove.

Referring to FIG. 9, an optical fiber cable 130 is shown according to anexemplary embodiment. Cable 130 is substantially the same as cable 10except as discussed herein. In this embodiment, cable 130 includes aplurality of optical transmission units, shown as unbundled subunits 50.In cable 130, subunits 50 are not surrounded and group by bundle jacketslocated within cable jacket 12.

As shown in FIG. 9, subunits 50 within cable 130 are arranged into aninner group 132 of subunits 50 and an outer group 134 of subunits 50. Ingeneral, inner group 132 is located in the central region of bore 16,and outer group 134 is located around and surrounding inner group 132.In the specific embodiment shown, cable 130 includes five subunits 50within inner group 132 and eleven subunits 50 within outer group 134. Insome such embodiments, each subunit 50 includes 12 optical fibers 58,such that cable 130 includes a total of 192 optical fibers. In variousembodiments, cable 130 may be configured to include between 150 and 250total optical fibers. In various embodiments to account for thedifferent fiber counts, inner group 132 may include three, four, etc.subunits 50 and outer group 134 may include less than eleven subunits 50or more than eleven subunits 50. While the embodiments discussed hereinrelate primarily to a cable having two groups or layers (an inner groupand an outer group) of subunits 50, in other embodiments, cable 130 mayinclude three, four, five or more concentric groups of subunits 50.

Similar to the wrapped bundles shown in FIG. 2, in various embodiments,both inner group 132 and outer group 134 of subunits 50 are wrapped,twisted or stranded to form a wrapped pattern within bore 16. Similar tothe wrapped patterns of bundles 20 discussed above, inner group 132 ofsubunits 50 are wrapped around each other forming a first wrappedpattern, and outer group 134 of subunits 50 are wrapped around innergroup 132 forming a second wrapped pattern. In various embodiments, thefirst wrapped pattern and second wrapped pattern each include at leastone spirally wrapped or twisted portion. In various embodiments, thefirst wrapped pattern of inner group 132 is different from the secondwrapped pattern of outer group 134. In general, the wrapped patterns ofinner group 132 and outer group 134 are selected such that the length ofthe subunits 50 (and consequently lengths of the optical fibers withineach subunit 50) are substantially the same as the other subunits 50 andother fibers of cable 130 (e.g., lengths of all subunits and all fibersof cable 130 are within 0.6% of each other and more specifically within0.1% of each other, as discussed in more detail below).

In general, the equal lengths between the inner group 132 and outergroup 134 are achieved through the inner group 132 having a tighterspiral pattern than outer group 134, and thus the tighter wrappedpattern of inner group 132 accounts for the smaller diameter of group132 as compared to outer group 134 resulting in the substantially samelengths of subunits and fibers between inner group 132 and outer group134. In a specific embodiment, the wrapped patterns of inner group 132and outer group 134 are selected such that the lengths of subunits 50 ofeach group are substantially the same as the other subunits 50 within atleast one, 1 meter section of cable 130.

In various embodiments, the differential wrapping between inner group132 and outer group 134 provide for a cable 130 that allows for a highfiber density cable with characteristics suitable for use in indoor datacenter applications. The substantially equal lengths of subunits 50 (andof optical fibers within the bundles) between inner group 132 and outergroup 134 results in a cable 130 with relatively low skew between thefibers of different subunits 50. This may facilitate usage of cable 130in conjunction with certain data center communications equipment, forexample parallel optics transmission equipment. In various embodiments,this stranding arrangement results in a cable 130 that has relativelylow skew meaning that the difference in transit time for opticalcommunication signals traveling in the optical fibers of outer group 134versus the transmit time for optical communication signals traveling inthe optical fibers of inner group 132 is less than 20 picoseconds/meterof cable (ps/m) and more specifically is less than 10 ps/m. In addition,the substantially equal length of subunits 50 (and optical fibers withinthe subunits) between inner group 132 and outer group 134 results insubstantially even tension distribution between the optical fibers ofouter group 134 and inner group 132.

Referring to FIG. 9, cable 130 includes at least one first tensilestrength strand, shown as a plurality of yarn strands 160, locatedwithin bore 16 of cable jacket 12 but outside of subunits 50. In generalyarn strands 160 provide substantially the same functions as bundle yarnstrands 60 discussed above, but without the bundle jackets associatingone or more yarn strands 160 with particular subunits 50. In theembodiment of FIG. 9, yarn strands 160 are located within anddistributed throughout bore 16 without grouping or association withparticular subunits 50. In various embodiments, yarn strands 160 may bearranged in a group or layer in the center of bore 16, in a group orlayer between inner group 132 and outer group 134, and/or in a group orlayer between outer group 134 and the inner surface of jacket 12. Insome such embodiments, cable 130 does not include a central strengthmember, such as a glass-reinforced plastic (GRP) rod, present in thecenter of many optical fiber cables.

In various embodiments, yarn strands 160 are unstranded (e.g., are notwrapped around the outside of subunits 50) such that yarn strands 160are substantially the same length as bore 16 and as cable jacket 12. Aswill be understood, in this arrangement, because subunits 50 arestranded in a wrapped pattern, the total axial length of yarn strands160 is less than the total axial length of subunits 50 and is less thanthe total axial length of optical fibers 58 within each subunit. Invarious embodiments, the total axial length of yarn strands 160 isbetween 0.05% and 0.4% and more specifically between 0.1% and 0.2% lessthan the total axial length of subunits 50 and the total axial length ofoptical fibers 58 within each subunit. As explained in more detailbelow, this arrangement results in a cable in which tension applied tothe cable is primarily transmitted by and experienced by yarn strands160 rather than optical fibers 58.

In various embodiments, yarn strands 160 may be any suitable tensilestrength yarn or fibrous material used in cable construction. In variousembodiments, yarn strands 160 are formed from an aramid yarn material.In other embodiments, the tensile strength strands of cable 130 may befiberglass yarn, poly(p-phenylene-2,6-benzobisoxazole) yarn sold underthe trade Zylon, polyester-polyarylate liquid crystal polymer fiber soldunder the trade name Vectran, or other high strength tensile yarns.

Referring to FIG. 10, an optical fiber cable 140 is shown according toan exemplary embodiment. Cable 140 is substantially the same as cable130 except as discussed herein. Cable 140 is a 288 fiber cable thatincludes nine subunits 50 in inner group 132 and fifteen subunits 50 inouter group 134. As shown in FIG. 10, cable 140 may include a group ofyarn strands 160 located in the center of inner group 132, and in thisembodiment, subunits 50 of inner group 132 may be stranded around thecentral group of yarn strands 160. As shown in FIG. 10, in place of orin addition to the central group of yarn strands 160, cable 140 mayinclude additional yarn strands 160 located between inner group 132 andouter group 134 and between outer group 134 and cable jacket 12.

Referring to FIG. 11, an optical fiber cable 150 is shown according toan exemplary embodiment. Cable 150 is substantially the same as cable140 except as discussed herein. As shown in FIG. 11, cable 140 mayinclude an elongate central strength member 152, such as a GRP rod,steel rod, etc., located in the center of inner group 132. In thisembodiment, subunits 50 of inner group 132 are stranded around strengthmember 152. As shown in FIG. 11, cable 150 may include yarn strands 160located between inner group 132 and outer group 134 and between outergroup 134 and cable jacket 12.

Referring to FIG. 12, an optical fiber cable 170 is shown according toan exemplary embodiment. As shown in FIG. 12, cable 170 may be free ofan elongate central strength member, such as a GRP rod, steel rod, etc.,located in the center of inner group 132. In this embodiment, subunits50 of inner group 132 may be stranded around a central strength member172 that may be an aramid yarn strand, for example. As shown in FIG. 12,cable 170 may include a third outer group 136 of stranded subunits 50 inwhich the pitch length of the third outer group 136 is greater than thepitch length of the outer group 134 such that the length of the fibersin the third outer group 136 are substantially the same as the length ofthe fibers in the inner group 132 and outer group 134. The third outergroup 136 may be wrapped in an SZ wrapped pattern (also referred to asan SZ stranding pattern). As also shown in FIG. 12, binder yarn strands160 may be located between inner group 132 and first outer group 134,between outer group 134 and second outer group 136, and between secondouter group 136 and cable jacket 12.

In various embodiments, subunits 50 can include a wide variety ofoptical fibers including multi-mode fibers, single mode fibers, bendinsensitive fibers, etc. In various embodiments, cable jacket 12, bundlejacket 40 and subunit sheath 52 may be a variety of materials used incable manufacturing, such as medium density polyethylene, polyvinylchloride (PVC), polyvinylidene difluoride (PVDF), nylon, polyester orpolycarbonate and their copolymers. In addition, the material of cablejacket 12, bundle jacket 40 and subunits sheath 52 may includequantities of other materials or fillers that provide differentproperties to the material of cable jacket 12. For example, the materialof cable jacket 12 may include materials that provide for coloring,UV/light blocking (e.g., carbon black), fire resistance as discussedabove, etc.

While the specific cable embodiments discussed herein and shown in thefigures relate primarily to cables, bundles and subunits that have asubstantially circular cross-sectional shape defining substantiallycylindrical internal bores, in other embodiments, the cables, bundlesand subunits discussed herein may have any number of cross-sectionshapes. For example, in various embodiments, cable jacket 12, bundlejacket 40 and subunits sheath 52 may have an oval, elliptical, square,rectangular, triangular or other cross-sectional shape. In suchembodiments, the passage or lumen of the cable jacket 12, bundle jacket40 and subunits sheath 52 may be the same shape or different shape thanthe shape of cable jacket 12, bundle jacket 40 and subunits sheath 52.In some embodiments, cable jacket 12, bundle jacket 40 and subunitssheath 52 may define more than one channel or passage. In suchembodiments, the multiple channels may be of the same size and shape aseach other or may each have different sizes or shapes.

In accordance with yet other aspects of the present disclosure, as shownin FIG. 13, for example, an optical fiber cable 200 may be a high fibercount cable (e.g., 576 fibers) that is constructed by helicallystranding four subunits 50 together with a short lay length to form astranded subunit group 53. Because the of helical stranding with shortlay length, the stranded subunits 50 are sufficiently bound togetherthat a bundle jacket 40 is no longer necessary to hold the subunits 50together. In accordance with yet other aspects of the presentdisclosure, a plurality of the stranded subunit groups 53 may then bestranded together to form a stranded cable core 55 comprised of theplurality of stranded subunit groups 53. For example, in FIG. 13, twelvestranded subunit groups are shown forming the stranded cable core 55inside the bore 16 of cable jacket 12. As noted infra, aramid yarn maybe incorporated as strength members in or around the subunits 50, thestranded subunit groups 53, and/or the stranded cable core 55.

The optical transmission elements discussed herein include opticalfibers that may be flexible, transparent optical fibers made of glass orplastic. The fibers may function as a waveguide to transmit lightbetween the two ends of the optical fiber. Optical fibers may include atransparent core surrounded by a transparent cladding material with alower index of refraction. Light may be kept in the core by totalinternal reflection. Glass optical fibers may comprise silica, but someother materials such as fluorozirconate, fluoroaluminate andchalcogenide glasses, as well as crystalline materials such as sapphire,may be used. The light may be guided down the core of the optical fibersby an optical cladding with a lower refractive index that traps light inthe core through total internal reflection. The cladding may be coatedby a buffer and/or another coating(s) that protects it from moistureand/or physical damage. These coatings may be UV-cured urethane acrylatecomposite materials applied to the outside of the optical fiber duringthe drawing process. The coatings may protect the strands of glassfiber. In addition to the subunits 50 and bundles of subunits 50discussed above, optical transmission units as discussed herein mayinclude optical fiber ribbons, tight-buffered optical fibers, opticalfiber micromodules, etc.

Unless otherwise expressly stated, it is in no way intended that anymethod set forth herein be construed as requiring that its steps beperformed in a specific order. Accordingly, where a method claim doesnot actually recite an order to be followed by its steps or it is nototherwise specifically stated in the claims or descriptions that thesteps are to be limited to a specific order, it is in no way intendedthat any particular order be inferred. In addition, as used herein, thearticle “a” is intended to include one or more than one component orelement, and is not intended to be construed as meaning only one.

It will be apparent to those skilled in the art that variousmodifications and variations can be made without departing from thespirit or scope of the disclosed embodiments. Since modifications,combinations, sub-combinations and variations of the disclosedembodiments incorporating the spirit and substance of the embodimentsmay occur to persons skilled in the art, the disclosed embodimentsshould be construed to include everything within the scope of theappended claims and their equivalents.

What is claimed is:
 1. An optical communication cable comprising: acable jacket forming a central bore; a plurality of optical fiberbundles, each optical fiber bundle including a bundle jacket extrudedaround a plurality of optical fiber subunits, each optical fiber subunitcomprising a plurality of elongate optical fibers; and an armor layersurrounding the plurality of optical fiber bundles; wherein a definednumber of optical fiber bundles are stranded together to form an innergroup of optical fiber bundles having a first wrapped pattern group;wherein a plurality of the optical fiber bundles are stranded togetheraround the first inner group to form an outer group of optical fiberbundles having a second wrapped pattern; and wherein each bundle jacketcomprises an extruded thin film that when cool provides an inwardlydirected force onto the plurality of optical fiber subunits to hold theplurality of optical subunits together to form a cohesive unit.
 2. Theoptical communication cable of claim 1, wherein the plurality ofelongate optical fibers comprises a plurality of twelve fiber subunits.3. The optical communication cable of claim 1, further comprising: awater blocking layer surrounding the plurality of optical fiber bundles.4. The optical communication cable of claim 2, further comprising atleast one connector coupled to the plurality of twelve fiber subunits.5. The optical communication cable of claim 1, wherein the firstwrapping pattern and the second wrapping pattern comprise an SZ wrappedpattern.
 6. The optical communication cable of claim 1, wherein thecable jacket has a cable jacket thickness and the bundle jacket has abundle jacket thickness, and wherein the cable jacket thickness isbetween 0.1 mm and 3 mm and the bundle jacket thickness is between 0.1mm and 0.8 mm.
 7. The optical communication cable of claim 1, whereinlengths of all optical fiber bundles and all optical fibers are within1.5% of each other.
 8. The optical communication cable of claim 1,wherein the bundle jacket comprises a fire resistant polyethylene,polypropylene, or PVC.
 9. The optical communication cable of claim 1,wherein the inner group comprises three optical fiber bundles and theouter group comprises nine optical fiber bundles.
 10. The opticalcommunication cable of claim 1, wherein the armor layer comprises acorrugated sheet of metal material having an alternating series ofridges and troughs.
 11. The optical communication cable of claim 10,wherein the metal material is steel.
 12. The optical communication cableof claim 1, wherein the armor layer comprises a plastic material havinga modulus of elasticity over 2 GPa.
 13. The optical communication ofclaim 10, wherein the outer cable layer comprises an extruded materialhaving at least one embedded access feature.
 14. The opticalcommunication cable of claim 13, wherein the access feature comprises adiscontinuous polymer feature coextruded with the material of the outercable layer.
 15. The optical communication cable of claim 13, whereinthe access feature comprises a ripcord or wire.